Chavez and his besmirched strength and conditioning coach, Angel Heredia, have expressed skepticism publicly about testing administered by the Voluntary Anti-Doping Association as they prepare for their May 6 catch-weight showdown in Las Vegas. Chavez and Heredia have implied Alvarez has something to hide by being particularly critical on social media about VADA testing their urine, but not their blood.

Both boxers agreed to be tested by Las Vegas-based VADA as part of their contracts for this HBO Pay-Per-View main event at T-Mobile Arena in Las Vegas.

“His declarations are very stupid,” Alvarez said through a translator Tuesday. “What he’s saying is very stupid. Simply put, very stupid, because we’re talking about VADA – the top agency, very professional. Whether they do blood, whether they do urine, they know what they’re doing.”

Alvarez (48-1-1, 34 KOs) reminded reporters, too, that while he has never tested positive for anything, Chavez (50-2-1, 32 KOs, 1 NC) has failed multiple tests, both for a performance-enhancing drug and marijuana, during his 13-year pro career.

“I haven’t tested positive ever in my career,” Alvarez said. “And he’s tested [positive] two or three times. So he should shut up and worry about himself, and stop saying those stupid things.”

The 31-year-old Chavez’s victory over Troy Rowland in November 2009 was changed to a no-contest because Chavez tested positive for using furosemide, a banned substance. Chavez admitted to taking that diuretic because he was struggling to make the middleweight limit of 160 pounds for that fight in Las Vegas.

The Nevada State Athletic Commission suspended Chavez for seven months and fined him $10,000 for failing that PED test. The NSAC later suspended Chavez for nine months and fined him $100,000 because he tested positive for marijuana following his September 2012 loss to then-middleweight champion Sergio Martinez in Las Vegas.

The NSAC initially fined Chavez a whopping $900,000 for failing a second drug test in Nevada, but later reduced that penalty to $100,000.

Keith Idec is a senior writer/columnist for BoxingScene.com. He can be reached on Twitter @Idecboxing.

What, are they not using blood testing at all? How common is it to only use urine tests? I've read somewhere that HGH doesnt show up much / long in urine, but shows up better in blood testing. Anyone know…